Organometallics 1996, 14, 423-426
423
Structures and Bond Energies of the Transition-Metal Carbonyls M(CO)s (M = Fe, Ru, Os) and M(C0)4 (M = Ni, Pd, Pt)l Andreas W. Ehlers and Gernot Frenking" Fachbereich Chemie, Philipps- Universitat Marburg, Hans-Meerwein-Strasse, 0-35032 Marburg, Germany Received July 26, 1994@ The equilibrium geometries of the transition-metal carbonyls M(C0)n (M = Fe, Ru, Os; n = 4 , 5 ) and M(CO), (M = Ni, Pd, Pt;n = 3 , 4 ) are calculated at the MP2 level using effective
core potentials for the metals and 6-31Wd) basis sets for C and 0. The first ligand dissociation energies of the saturated metal carbonyls are theoretically predicted using the coupled cluster theory (CCSD(T))approach. The calculated dissociation energies AlPg8(Fe(C0)5, 46.5 kcdmol; Ru(CO)&,30.9 kcaYmol; Os(CO)5, 42.4 kcaYmol; Ni(CO)d, 24.4 kcall mol; Pd(C0)4, 9.6 kcdmol; Pt(co)4,13.0 kcdmol) indicate that the second-row transition elements have the weakest carbonyl bond.
1. Introduction The accurate determination of thermochemical data for transition-metal complexes is a difficult problem for experimental and theoretical methods.2 In a recent publication we have shown that the metal-ligand bond lengths and first dissociation energies of MO(CO)~ and W(CO)6 are predicted with excellent accuracy a t the CCSD(T)//MP2 level of theory using effective core potentials for the metals and moderate basis sets for C and Oa3The calculated Cr-CO bond length of Cr(CO)6 was slightly too short and the bond energy too high.3 Here we report our results for the pentacarbonyls of the group 8 elements M(CO)5 (M = Fe, Ru, Os) and the tetracarbonyls of the group 10 elements M(C0)4 (M = Ni, Pd, Pt)using the same theoretical method as in our previous s t ~ d y . ~ 2. Methods The geometries are optimized at the MP24 level using an effective core potential (ECP) and a (44112111lN - 11)splitvalence basis set for the metals, which is derived from the (551 51N) minimal basis set optimized by Hay and Wadt5 (N = 5, 4, 3 for the first-, second-, and third-row transition metals, respectively). The ECPs are derived from nonrelativistic atom calculations of the first-row transition elements (Cr, Fe, Ni) and relativistic calculations of the second- and third-row transition elements (Mo, W, Ru, Os, Pd, Pt). A 6-31G(d) allelectron basis set is used for C and 0.6 This basis set combination is denoted BS 11. The dissociation energies are calculated using coupled-cluster theory with singles and Abstract published in Advance ACS Abstracts, December 1,1994. (1)Theoretical Studies of Organometallic Compounds. 10.Part 9: Blihme, M.; Frenking, G.; Reetz, M. T. Organometallics 1994,13,4237. (2)(a) Salahub, D. R., Zemer, M. C.,Eds. The Challenge of d and f Electrons: Theory and Computation; ACS Symposium Series 349; American Chemical Society, Washington, DC, 1989.(b) Marks, T.J., Ed. Bonding Energetics in Organometallic Compounds; ACS Symposium Series 428;American Chemical Society: Washington, DC, 1990. (3)(a) Ehlers, A. W.; Frenking, G. J. Am. Chem. SOC.1994,116, 1514.(b) Ehlers, A. W.; Frenking, G. J. Chem. Soc., Chem. Commun. 1993,1710. (4)(a)M~ller,C.; Plesset, M. S.Phys. Rev. 1934,46,618.(b) Binkley, J. S.; Pople, J. A. Znt. J. Quantum Chem. 1975,9, 229. (5)Hay, P. J.;Wadt, W. R. J. Chem. Phys. 1986,82,299. (6)Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56, 2257.
doubles and a noniterative estimate of triple substitutions (CCSD(T)).' Zero-point vibrational energies (ZPEs) are calculated at the Hartree-Fock level. The geometries have been calculated using the program TURBOMOLE.* For the CCSD(T)calculations the program ACES 119was employed. As in our previous study of M(CO)e compounds,3 we did not correct the calculated dissociation energies for the basis set superposition error (BSSE). There are two types of errors in calculations using a truncated basis set, i.e. the BSSE and the basis set incompletion error (BSIE). These two errors have opposite sign. Both errors can, in principle, be corrected by saturating the basis set. Correcting for the BSSE would leave the BSIE uncorrected. We think that for a comparison with experimental values directly calculated results should be used rather than estimated data.
3. Results and Discussion Table 1 shows the theoretically predicted and experimentally observed equilibrium geometries of the metal carbonyls. The theoretical and experimental first dissociation energies are shown in Table 2. The calculated and experimental bond energies for the hexacarbonyls M(CO)s are given for comparison. The theoretically predicted geometry of Fe(C0)5 at the MP2/II level has Fe-CO bonds which are clearly too short. In particular, the axial Fe-CO bond is calculated to be significantly shorter (1.688 A)than is experimentally observed (Table 1). This is because the HartreeFock wave function is a very poor approximation for the electronic structure of Fe(C0)5.1° The calculations predict that the axial Fe-C bonds are shorter than the
@
(7)(a) Cizek, J. J. Chem. Phys. 1966,45, 4256. (b) Pople, J. A.; Krishnan, R.; Schlegel, H. B.; Binkley, J. S. Znt. J. Quantum Chem. 1978,14,545. (c) Bartlett, R.J.; Purvis, G. D. Znt. J.Quantum Chem. 1978,14,561.(d) Purvis, G.D.; Bartlett, R. J. J. Chem. Phys. 1982, 76, 1910.(e) Purvis, G.D.; Bartlett, R. J. J. Chem. Phys. 1987,86, 7041. (8)(a) Hgser, M.;Ahlrichs, R. J . Comput. Chem. 1989,10,104.(b) Ahlrichs, R.;Blir, M.; Htiser, M.; Horn, H.; KiSlmel, C. Chem. Phys. Lett. 1989,162, 165. (c) Horn, H.; Weiss, H.; Htiser, M.; Ehrig, M.; Ahlrichs, R. J. Comput. Chem. 1991,12,1058.(d) Htiser, M.;Almlaf, J.; Feyereisen, M. W. Theor. Chim. Acta 1991,79,115. (9)An ab initio program written by: Stanton, J. F.: Gauss, J.; Watts, J. D.; Lauderdale, W. J.; Bartlett, R. J. ACES 11; Univerity of Florida, Gainesville, FL, 1991.
Q276-7333/95/2314-Q423$Q9.QQlQ 0 1995 American Chemical Society
424 Organometallics, Vol. 14,No. 1, 1995
Ehlers and Frenking
Table 1. Calculated and Experimental Bond Lengths Fe(C0)p
Ru(C0)5"
sYm
state
m-c1
m-c2
D3h
'Ai'
1.688 1.877 1.798 1.77 1.807 1.811(2) 1.943 1.95 1.941(13) 1.963 1.98 1.982(20) 1.726 1.951 1.942 1.801 1.831 1.873 1.817(2) 1.825(2) 2.013 2.032 1.966 2.100 1.796 1.981 1.935
1.766 1.847 1.836 1.79 1.827 1.803(2) 1.952 1.96 1.961(13) 1.945 1.99 1.937(19) 1.713 1.904 1.909
D3h
'Ai' 'Ai'
'AI 'Ai 'Ai 'AI
'AI 'Ai 'Ai' 'Ai' 'Ai'
(A) of the Metal Carbonyls
rcl-ol 1.176
rc2-02 1.166
1.152 1.117(2) 1.162
1.152 1.133(3) 1.165
1.126(9) 1.163
1.127(10) 1.168
1.130(52) 1.170 1.161 1.165 1.162
1.13l(35) 1.178 1.171 1.172
1.127(3) 1.122(2) 1.157 1.160 1.163 1.158 1.161
method
ref
MP2 MCPF CCI DFT exptl exptl MP2 DFT exptl MP2 DFT exptl MP2 MP2 MP2 MP2 CCSD(T) MP2 exptl exptl MP2 MP2 MP2 MP2 MP2 MP2 MP2
this work 10b
The first bond length refers to the axial bond and the second to the equatorial bond. Calculated bond angle a(C1-Fe-Cl') = 135.9". Calculated bond angle a(Ct-Ru-C
